The Chemistry Corollary
by starfish001
Summary: Sheldon watches as Penny and Leonard self-destruct...


**Christmas 2009**

The festive period isn't very festive, what with all the arguments. Sheldon listens to them from the sanctuary of his room and gets Penny a book titled _"__Alcohol Problem Explained: How to Stop Drinking and Start Living"_ since he notices that most of her time with Leonard is spent intoxicated. It earns him an icy stare and a brittle grin. He does the math; over the last few months Leonard and Penny have split up and gotten back together an average of 0.7 times a fortnight. He stops offering Leonard advice after being told he _couldn't possible understand _for the fourteenth time. Leonard is right; he doesn't understand. He researches dysfunctional relationships online and still doesn't understand.

**February**

Penny starts seeking him out after their arguments, whilst Leonard, exasperated with his inability to offer any support, seeks out Raj. He offers her no opinion on their fights, preferring to remain neutral, but she doesn't seem to mind. Usually they sit watching Dr Who re-runs, him explaining the plot and the science of time travel, her knee lightly brushing his as she sits quietly, listening if not understanding. It is not physical comfort in the traditional sense, but it is all he can offer. She usually leaves looking less pressured, so he determines it to be enough.

**May**

Leonard is now pretty much living with Penny, but keeps paying his share of the rent on Sheldon's place. He spends several nights a month there after arguments, so it makes sense to have a bolt-hole even if he does have to put up with Sheldon's pointed looks when he storms back in. Sometimes Sheldon hears them having make-up sex and buries his head in the pillow. He eventually invests in some ear plugs, sacrificing aural health for the sake of his sanity.

**June**

Penny slowly starts spending more time with him when Leonard isn't about. They still bicker, and sometimes argue passionately, but both enjoy the challenge. She still wants to kill him sometimes, and he still gets exasperated by some of the things she doesn't know. He sets about educating her in his passions; it's from him she learns about the 'geek' stuff Leonard seems embarrassed by. In turn, she introduces him to pop culture and the genius of Radiohead. He grudgingly admits they may have some merit and secretly sets about purchasing their back catalogue.

He realises he is starting to look forward to their time alone together, and tentatively notices that she appears to be sacrificing time with her girlfriends in favour of spending it with him. He feels an odd sensation in his belly at the thought but refuses to let himself think about the possible implications. That sort of thing doesn't happen to him.

And anyway, Leonard is his best friend.

Penny doesn't realise she is spending more time with Sheldon than with almost anyone else. At least, not until Leonard gives her a funny look when she turns down a night out dancing in favour of a Dr Who marathon with Sheldon. She can see him debating with himself over a question he doesn't really want answered, and it suddenly hits her how it must look.

She tries to bury the thought that _how it looks_ might actually be _how it is_. It's irrelevent, really; a harmless distraction. A crush. And anyway, it's not like Sheldon is ever going to reciprocate.

It's harmless.

**July**

They all go to Comic-Con. Sheldon feels his head spin at the sight of Penny in her Black Canary outfit and wonders what's happening to him; he spends the day in confusion, avoiding her and Leonard in their currently amiable private world. Eventually though she gets frustrated and corners him, demanding an explanation for his sullenness. For once, his mind can't provide him with an answer that wouldn't destroy his neatly ordered world. Instead he mutters his apologies, pleading illness, his eyes begging her not to press the issue. She stares at him searchingly, and for a brief moment he wonders if she _knows_, but then she lets it drop. He pushes the thoughts out of his head and spends the next few months trying to forget the image of Penny in fishnets.

**November**

The arguments have reduced; Sheldon uncharitably considers it to be a sign that they just don't care enough to argue anymore. Still, despite his protests Leonard drags him shopping for an opinion on an engagement ring. Whilst the other man haggles over the price of a gold diamond solitaire, Sheldon (thinking_ Penny doesn't like yellow gold _but electing not to tell him) sees a delicate bracelet set with her birthstone and quickly buys it. It is impulsive, not to mention expensive, but he reasons Christmas is coming and he never did properly repay her for the Nimoy napkin.

**Christmas 2010**

Penny gives Sheldon a copy of X-Men #140 for Christmas, which he thanks her for profusely. From nowhere, she pulls out a sprig of mistletoe and, grinning, plants a kiss on his rapidly flushing cheek. He feigns gentle irritation as he feels his stomach churn. He gives her the bracelet he bought and then it's his turn to hide his delight at the astonished look on her face. She hugs him tightly and he doesn't pull away, stomach now somersaulting. Leonard looks on, and silently slips the engagement ring back in his pocket.

That night, she sits on the couch whilst Leonard snores gently in the bedroom. She stares at the bracelet; it's beautiful, and thoughtful, and so amazingly unexpected coming from him. Eventually she stands and wipes her face; she must have been crying, though she hadn't noticed through her spinning thoughts. She lies awake next to Leonard for hours before deciding she simply has an overactive imagination; this is Sheldon, and the only explanation is that she's reading too much into his gesture of friendship.

**New Year**

Leonard proposes at midnight. She asks for some time to think, trying to ignore the hurt look on his face. A day later, drunk, she corners Sheldon and asks him for a reason not to marry Leonard. He can think of a hundred, but offers her none.

His feelings are irrelevant; he will never be able to give her what she needs.

She tells Leonard 'yes'.

**February**

She throws herself into wedding plans and takes Leonard to meet her family. For once they are on their best behaviour, but her mom drags her aside on their last day together and asks if she's sure about this guy. She tells her mom she loves him. It's not a lie. It's not quite the whole truth either.

Sheldon mopes about the apartment the whole time they are away. Raj and Howard wonder what's gotten into him and eventually put it down to some sort of cyclical hormonal fluctuation affecting the homo novus. Or, as Howard puts it, _"maybe in his species it's the men who ride the crimson wave…"_

**March**

Penny gets her first proper paid acting job and they celebrate at a Sheldon-approved restaurant. They all have too much to drink; Leonard passes out on Sheldon's couch when they get back. Penny herself can hardly walk in a straight line, so Sheldon half-drags, half-carries her to Leonard's room. As she reaches the bed she stumbles and he lunges to catch her, but is instead pulled down on top of her. The air is suddenly tense; he feels her body underneath him and an instinct which has till now lain dormant suddenly starts nudging the back of his brain. His eyes meet hers, their faces inches apart. Both are breathing heavily and for a long moment neither makes any attempt to move. When he does, it is to gently brush a stand of golden hair from her face, and she closes her eyes at the touch of his fingers. He swallows hard; she is so beautiful.

But she is also Leonard's. He pulls away suddenly, not seeing the look of longing on her face, and turns to leave.

"Sheldon…"

He turns back, and she sees the pain and confusion on his face. His voice is low. "Yes Penny?"

She pauses, debating herself. "Thank you. For looking after me."

She watches him nod and leave, burying the one word she wanted to say.

_Stay_.

**April**

Penny is in Sheldon's doorway, clutching a white plastic stick and sobbing. It takes him a minute to realise what it is, then he feels sick; he elects to put it down to the unsanitary way she is waving the thing in his face. She flings herself into his arms and he holds her awkwardly, feeling like something in his chest is twisting. He asks how Leonard took the news; she hasn't told him yet, is scared of his reaction. Knows how pleased he will be. She asks that he keeps it a secret until she's decided what to do and he panics, but the look on her face makes him hesitantly agree. She hugs him tight and he feels her tears on his cheek.

He'll keep her secret.

**May**

As it turns out, he doesn't have to keep it for long. Penny loses the baby soon after. Though she hadn't yet decided what to do, she feels the loss. She can't hide her sadness from Leonard and they fight; he is upset she hid the pregnancy from him and she can't even explain why she didn't tell him earlier. She finally decides she can't do this anymore; the arguing, their emotional rollercoaster of a relationship. She tries to give him back the engagement ring and he storms out; stays the night at Raj's, she figures. She again ends up on Sheldon's couch, pouring her feelings onto him where they lay like oil on water. He asks if she loves Leonard; she does, she says.

She doesn't add that she loves _him_ more; that the feelings for Leonard are nothing compared to those she has buried for him. She knows those aren't feelings he can return. But the thought of being alone right now fills her with dread.

The next day Leonard comes back; both are full of apologies. Crying, she tells him she's sorry, wants to try again.

Crying, he tells her he slept with Leslie last night.

This time, she _throws_ the ring at him.

**June**

Penny is hammering on Sheldon's door in a way that suggests she's inebriated again. He hasn't seen her since the split; she's been avoiding the apartment since Leonard moved back in. He's missed her, and has been doing his own guilty share of evading Leonard in order to avoid confronting his traitorous thoughts. But tonight Leonard is working and now she's in his doorway, looking red faced, blotchy and utterly beautiful.

"You know what bugs me?" she starts speaking before he even invites her in and continues before he can answer.

"The whole time I was with him, there was something I wanted to do. Something I wanted to do so, so badly. But something that I _didn't_ do, because I'm not like that. That's not me. And then…then he went and did _that_."

Sheldon looks at her uncomprehendingly. "Penny, you're not making any sense. What did you want to do?"

"_This."_

Suddenly she is on her toes, her arms around his neck as she pushes her lips against his. His hands come to rest spontaneously, tentatively, on her waist as he kisses her back. It is uncertain and inexperienced, but it is incredible. _She_ is incredible. His head feels light and he wonders if one can experience syncope from a kiss.

All too soon she breaks it off and rests her forehead against his, her eyes closed. He doesn't dare move for fear of ending the moment. They stay like that for what feels like an age before she pulls away, her hands lingering against his chest, stroking, tracing the outline of the pattern on his shirt. Finally she looks up.

"I don't know what to do, Sheldon. Tell me what to do."

He knows she is talking about her and Leonard, about her and _him_. And he can't give her the answer, no matter how much he wants to. She needs to figure it out herself. But for now…

"Kiss me again" he whispers.

And she does.

**July**

Leonard moves out when they tell him. He is probably the least surprised of them all by the revelation; he has been ignoring the signs for a long time now. There's surprisingly little animosity, though, and he moves out not through anger but simply through a desire not to have their relationship thrust in his face. He had loved Penny and deeply regretted what had happened, but couldn't deny that it had been a difficult few years and the most surprising thing is just how relieved he feels now it's over. He half expects the relationship to end quickly; after all, he is Sheldon's best friend and even he finds him…difficult. But watching them together, he decides, they _do _make a strangely good couple.

And he has to admit, it's good to see someone other than him feel Penny's wrath in the heat of an argument.

**A year later**

Sheldon spends two months hunting for the perfect ring. On a visit, he wins her uncertain family over by asking their permission before he proposes. Her father still isn't sure (_that boy's too damn smart for his own good_, he mutters as her mom shushes him) but he can see how happy she is and grudgingly admits she could do worse. Her mom looks at her glow and doesn't ask if she's sure this time.

He proposes at Comic-Con, almost shaking with unanticipated fear. He needn't have worried; this time, she says yes without hesitation, flinging her arms around his neck and wrapping her legs around his waist. The sight of Spock and Yeoman Rand in a passionate embrace raises some eyebrows and garners a round of applause.

He kisses her, something which never fails to make her feel giddy. And when he whispers _I love you_ in her ear she thinks she has never been so happy.

When she whispers it back, he decides he is the luckiest man alive.


End file.
